Low oil detector with automatic reset

Abstract

An optical liquid level sensor for distinguishing between the presence of oil and vapor within a compressor crankcase. The sensor has a light transmitting window positioned to interface the crankcase interior and a planar side facing the crankcase exterior. A light source and a light sensor are both positioned adjacent the exterior face of the window. The sensor has a first condition when the prismatic face is immersed in oil and a second condition when the prismatic face is immersed in vapor. An electronic circuit having a dual MOSFET switch for alternating current is mounted adjacent the light source and sensor. The circuit provides power to the source and monitors the sensor. When the sensor is in the first condition, the circuit closes the switch. When the sensor detects the second condition, the circuit starts a timer and continuously tests the condition of the sensor. If the first condition is detected, the timer resets to its initial value. If the second condition continues for the full time period, the circuit opens the switch. On the opening of the switch, the circuit continuously tests for the condition of the sensor. If the sensor returns to the first condition, the circuit closes the switch. An external switch is provided to manually reset the timer to its initial value and cause the switch to close for the time period.

I claim: 
     
       1. An oil loss protection system for use with an alternating current supply, the system including an oil loss sensing module for a refrigeration compressor having an oil containing reservoir, the reservoir including a wall, the wall having an oil side and an outside, the oil within the reservoir having a higher and a lower oil level, actuating means, controlled by the oil loss sensing module, for starting and stopping the compressor, the oil loss sensing module comprising: a) a fitting positioned in operative relation to the oil level,   b) optical means for interfacing and interacting with the oil level, the optical means comprising: window means sealed to the fitting, the window means having an oil side and a circuit side, the window means having a prismatic surface positioned on the oil side and subject to the oil level and a substantially planar surface positioned on the circuit side,     c) encapsulated electronic circuit means having an alternating current supply and an alternating current output, the encapsulated circuit means positioned substantially adjacent the planar surface of the window means, the circuit means comprising: rectifying means for supplying direct current to the circuit means,   a light source positioned to transmit light to the planar surface of the window means,   a light sensor positioned to receive light from the planar surface of the window means and to respond to a lower and a higher oil level,   alternating current switch means for controlling the alternating current output and thereby starting and stopping the compressor actuating means,   resettable timing means responsive to the light sensor for opening the switch means and thereby stopping the compressor actuating means on the elapse of a predetermined time period after the sensor has responded to a lower oil level, and   means responsive to the light sensor for resetting the timing means and for closing the alternating current switch means, thereby starting the compressor actuating means, on a condition of higher oil level occurring after the timing means has responded to a condition of lower oil level and caused the switch means to open.     
     
     
       2. An oil loss protection system as recited in claim 1, where the light source is the rectifying means. 
     
     
       3. An oil loss protection system as recited in claim 2 where the alternating current switch means comprises at least two metal-oxide-semi-conductor-field-effect-transistors (MOSFETs). 
     
     
       4. An oil loss protection system as recited in claim 3 further providing that each MOSFET includes connections identified as Source, Drain and Gate, and further providing that two MOSFET's are connected Source to Source between the actuating means and the alternating current supply. 
     
     
       5. An oil loss protection system as recited in claim 4 further providing that the circuit means includes a common connection and the joined Source connections of the MOSFETs are connected to said common connection. 
     
     
       6. An oil loss protection system as recited in claim 5 further including switch means external to the encapsulated circuit means, said switch means being positioned in the alternating current supply for temporarily interrupting power to the circuit means, whereby the timing means is reset and the actuating means re-energized for the duration preset by the timing means. 
     
     
       7. An oil loss protection system as recited in claim 6 where the oil sensing module is positioned within the reservoir. 
     
     
       8. An oil loss protection system as recited in claim 6 where the oil sensing module is positioned in the reservoir wall with the circuit side on the outside. 
     
     
       9. An oil loss protection system as recited in claim 6 where the external switch means is a manually actuated normally closed switch. 
     
     
       10. An oil loss protection system as recited in claim 6 where the external switch means is a temperature control thermostat.